Fire control computer



v K. 6 b 7 1 x 9 MB. M fw 3 9 J 2 n O 5 d 0 4 w 5 3 2 Aug. 1945- G. A. CROWTHER FIRE CONTROL COMPUTER Filed Feb. 11 1941 3 Sheets-Sheet 1 INVENTOR GeorgeA Crawflwr AHORNEY 4J3. HUJB I Um 1945' G. A. CROWTHER FIRE CONTROL COMPUTER 3 Sheets-Sheet 2 Filed Feb. 11, 1941 IN VEN TOR GemyaAflrowtMr Q ATTORNE L'JUJ: i

Aug. 14, 1945. s. A. CROWTHER FIRE CONTROL COMPUTER Filed Feb. 11, 1941 3 Sheets-Sheet M ON E55.ECEEEZEEC 3 mm 3 N l a Mm lm uzrrruo uni. N

Patented Aug. 14, 1945 FIRE CONTROL COMPUTER George Alfred Crowther, Manhasset, N. Y., as-

signor to Ford Instrument-Company, Ina, Long Island City, N. Y., a corporation of New York Application February 11, 1941, Serial No. 378,367

5 Claims.

This invention relates to gun-fire control computers and particularly to that type of computers used to control the firing of guns against aircraft.

The problem of the control of gun-fire against aircraft may be divided into two classes; (1) where the aircraft or target is approaching directly towards its objective or the point of observation and the firing gun, and (2) where the target is passing at a distance to one side or the other of the observing and firing point. The invention herein disclosed is applied to the first mentioned class. It will of course be understood that some of the principles thereof are applicable to the solution of problems of the second mentioned class.

In considering the solution of the problem of antiaircraft fire control to which this invention is applied as one embodiment thereof, it is assumed that the target is directly approaching its objective, which is the point of observation and the point of firing of the gun, at a substantially constant height above the horizontal plane of the objective, such as would be done in horizontalbombing of a selected point. Upon the picking up of the target by observers at the objective, the direct or slant range of the target and its elevation above the horizontal, expressed in angular units, are observed by instruments Well known in the art and from the observed data the height of the target and the horizontal range may be determined, or if the height of the target is known or obtained by observations and the elevation is observed, the direct or slant range and the horizontal range may be determined.

From experimental data obtained during target practices, the most efiective ranges of the guns are known as well as the time in seconds required to set and adjust the sights and the fuses of the projectiles and to load and fire the projectiles. In this specification, the time required to set the observed values into the mechanisms, for the mechanisms to calculate the advance range or fuse setting and the sight angle, and the time required to adjust the sight and gun and load and fire the gun is defined as the preparation period of time. This preparation period is arbitrarily selected and is based upon experience under various circumstances of operation.

The object of the invention is to provide a mechanism settable in accordance with an observed range or height and elevation angle of an approaching aircraft target and settable in accordance with the speed of the target and the selected preparation period of time followingthe instant of the observations, for computing the sight angle or difierence in elevation of the gun and the line of sight at the instant of firing and,

the time-setting values of the fuses of the fired projectiles.

Mechanisms for accomplishing the objects of the invention and their operation will be understood by considering the following description and accompanying drawings in which:

Fig. 1 is an elevation side view of an aircraft target directly approaching an observing and firing point at a constant height and showing the consecutive angular and linear relations of the target to the observing and firing point;

Fig. 2 is a diagrammatic view of a mechanism to compute the values required in the control of the fire oi the gun; and

Fig, 3 is a diagrammatic view of a modification of the mechanism shown in Fig. 2.

Referring particularly to Fig. 1, an aircraft or target I is directly approaching the observing and firing point 0 at a constant height (H) above the horizontal 0-0 and at a horizontal speed of St.

When the target I reaches point A, observers at O observe the direct or slant range (R) and the elevation angle of the target (AI), from which the height (H) and the horizontal range (RH) may be calculated by the equations resulting from the right angle triangle 0AA of H =R sin A1 and RH =R cos A1, respectively. A is the projection of the point A on the horizontal 0-0.

The preparation period of time (X) is selected as required and multiplied by the speed of the target (St) to give the distance traveled by the target during the time (X) represented by the length of line AB, thus defining the point B at which the target I will be at the end of the preparation period. The value of the distance AB may be expressed by the equation AB=X'St (1) The horizontal range of target I at point B (EH3) is equal to the observed horizontal range minus the distance AB or From the right angle triangle OBB, the elevation of the target when at point B (A3) will be the angle whose tangent is the height divided by the horizontal range to the point B, or

BC=t-St (4) This distance determines the point of intercept (C) and a perpendicular dropped from C determines the point C. It is obvious that OC'represents the horizontal range to the point of intercept (RH2), and that 4 RH2=RH3(t-St) 5) The elevation angle of the point of intercept (A2) is obtained'from the right angle triangle C and is the angle whose tangent is th height divided by the horizontal range to the point of intercept (RH2) or A2--tan The'elevation of the gun abov the line of sight to the point B, to allow for the movement of the target during time of flight is known as vertical angular deflection (Ut) and may be expressed as It is obvious that the distance AC is equal to (X+t) St and that Also from ballistic tables and curves obtained from experimental data the correction in elevation,- known as super elevation (e), that must be applied to compensate for, the shape of the trajectory of the projectile, is known for various combinations of horizontal ranges and heights. The total elevation of the gun above the line of sight is known as sight angle (Us) and may be expressed as Us: Ut+e (9) The mechanism required for the mechanical solution of the problem as set forth in detail hereinbefore is connected as a closed or regenerative system, that is, one section of the mechanism modifles or partially controls the movement of a second section, and the output of the second section is combinedin or partially controls the movement of a third section and the output movement of the third'section is connected back to affect or modify the movement of the first or second section. Such mechanisms as a system are stable and operable, when the movement thus connected back to modify the input to a preceding section is only a small part of the total input to that section and therefore has a much reduced effect on the output of the section which is connected back. Referring particularly to Fig. 2, th vector inputs of the vector analyzer or component solver ,2 are the observed slant range (R) set in by handle 3 and shaft and the observed elevation of the-target (Al) from the point of observation (0), set in by handle 5 and shaft 6. The set in values of R and Al aremade visually available by dials I and 3 geared to shafts 4 and 5, respectively. The outputs of component solver 2 are shafts 9a and ID, the rotational positions of which represent height (H) and horizontal range (RH), re-

spectively. Shaft 9a is connected to shaft 9 through differential 9b the third side of which is shaft 90 to which is geared zero reader dial 9d.

Shaft 9 is moved by handle 9e to set the value of height into the rest of the mechanism, by bringing the zero reader dial 9d to its zero position by the connection of shaft 9 to the differential 9b. The value of height (H) set into the mechanism is indicated by the dial 9) geared to shaft '9. If height is known, instead of range, the height is set in by handle 9e and dial 9] to the observed value. Any displacement of the zero reader dial is removed by operating the range handle 3 to bring the zero reader dial back to zero. This will introduce a value of range (R) corresponding to the value of elevation AI and height (H) set into the mechanism.

The inputs of the conventional multiplier l2 are the estimated speed of the target (St) set in by handle l3 and shaft M and the sum of the preparation time (X) and the time of flight (t). The value of X is set in by handle [5, shaft I6, differential l1 and shaft I8. The set in value of X is made visually available by dial I9 geared to shaft IS. The set in value of St is made visually available by dial Ha geared to shaft M. The generation of the value of the time of flight (t) represented by the rotation of shaft 20 will be described hereinafter.

The output of multiplier l2, (X+t) St, is trans- "mitted by shaft 2| to differential 22 where it is combined with the motion of shaft l0 representing horizontal range (RH). The output of differential 22, RH(X+t) St or RH2 (see Equation 8) is transmitted by shaft 23 to a conventional three-dimensional cam unit, of which the other input is shaft 9 representing height (H). Cam 24 of this unit consists of a solid rotated by the shaft 23 representing horizontal range (RH2). The surfaces of the various lateral cross-sections of the solid along its axis form a cam surface to give to cam follower 25 a motion proportional to the time of flight of the projectile for the range represented by the rotational position of the cam and the value of height represented by the axial position of the follower 25. The cam follower 25 is positioned parallel to the axis of the cam 24 to engage the various lateral sections of the solid cam in accordance with the value of height (H) as represented by rotational position of the threaded portion of shaft 9, which engages the threaded carriage on which follower 25 is mounted for rotational movement. Cam follower 25 is kept in engagement with the cam surface by spring 26 and its motion is transmitted to elongated gear 21 on shaft 20 by the toothed sector 28 to which follower 25 is secured. Shaft 20 is connected to differential IT to introduce time of flight into multiplier l2 as previously described.

Shaft 23 representing horizontal range (RH2) is also connected as one input to position one of the component slides of a conventional vector solver 29. The input for positioning the other component slide of the vector solver is shaft 9 representing height (H). The output of vector solver 29 is shaft 30, which is driven by the vector gear, the rotational position of which represents the angle of the point of intercept (A2), as shown by Equation 6. The vector gear is provided with a radial slot in which is slidably mounted a pin 29a which projects through slots in the component slides. The radial position of the pin 29a and the angular position of the vector gear are determined by the intersection of the component slides.

and l The inputs of the conventional multiplier 3| are shaft l4 representing target speed (St) and shaft 26 representing time of flight. The output of multiplier 3| is shaft 32 the rotational position of which represents t-St. The motion of shaft 32 is combined with that of shaft 23 representing horizontal range (RH2) by differential 33 and the output of differential 33, shaft 34, is connected to vector solver 35 as one input thereto, the other input being shaft 9 representing height. The output of vector solver 35 is shaft 36, the rotational position of which represents the value of the elevation angle of the point of firing (A3). The value of A2 minus A3 is obtained by connecting shafts 30 and 36 to differential 31, the output of which is shaft 38. The rotational position of shaft 38 represents Ut (see Equation 7) The value of the super elevation (e) is obtained by the three dimensional cam 39, which is similar in construction and operation to cam 24, except the surface of cam 39 is such that the radial positions of the cam follower 40 relative to shaft 23 represent super elevation (e). The position of the cam follower 40 and the associated toothed sector controls the rotational position of the elongated gear 4| in accordance with the value of the super elevation (e) corresponding to the values of horizontal range and height represented by shafts 23 and 9 respectively.

The motion of shaft 42 which is driven by elongated gear 4| is combined with that of shaft 38 by differential 43, the output of which, shaft 44, represents the sight angle (Us). The sight angle is made visually available by dial 45 geared to shaft 46 which is connected to shaft 44 by differential 41. Arbitrary corrections in sight angle may be applied to shaft 46 by shaft 48 which is connected to differential 41, the other input of which is shaft 44. Shaft 48 is moved by handle 49. The values of the corrections are made visually available by dial 50 geared to shaft 48.

As the fuses of the projectiles are set in accordance with the time of flight (t), shaft 26 is connected to graduated dial 5| by differential 52 and shaft 53. The other input to differential 52, shaft 54, is provided to apply arbitrary corrections to dial 5|. Shaft 54 is moved by handle 55. The values of the corrections are made visually available by dial 56 geared to shaft 54.

It has been found that the deflection due to the drift of a projectile is substantially proportional to the super elevation (e) of the gun relative to the line of sight. Therefore dial 51, suitably calibrated from experimental data to give values of drift for corresponding values of super elevation, is connected to shaft 42 by shaft 58 through differential 59. Corrections in deflection may be added by moving handle 60 on shaft 6| which is connected to the third side of differential 59. The value of the corrections in deflection is made visually available by dial 62 geared to shaft 6|.

Figure 3 shows another embodiment of the invention to solve the same problem. Corresponding parts in Figs. 2 and 3 are similarly numbered.

In Fig. 3, vector analyzer 2 is of the visual type in which a disk 63 is rotated about its axis by shaft 6 in accordance with the observed elevation of the target (Al), the setting of Al being made visually available by an index mark 64 on the disk 63 cooperating with scale 65. Between index mark 64 and the center of disk-63 piration of one-half the barrage time.

is a radial scale 1| calibrated in director slant range (R). The values represented by the component slides of vector analyzer 2 are the height (H), which is setin by handle 92 on shaft 9 by which slide 66 is moved and horizontal range (RH) of point A (see Fig. 1) which is set in by handle 12 on shaft ID by which slide 69 is moved. The value of the set in value of height is made visually available by a stiff cross wire 61 secured to slide 66 and'cooperating with scale 68, which is graduated in terms of height. The value of the horizontal range (RH) of point A (see Fig. 1) is obtained by moving slide 69 and its stiff cross wire 10 until it intersects cross wire 61 where it passes over the range scale 1|. It is of course obvious that if the slant range and elevation of the target are observed, the value of AI is set in as previously described and slide 69 is moved until wire 16 intersects range scale 1| at the observed range. Slide 66 is then moved by shaft 9 until wire 61 is directly over the intersection of wire 10 and scale 1|.

Referring to Figs. 1 and 3, the value of the horizontal range (RH3) to the point B is obtained by subtracting distance AB, which represents the speed of the target (St) multiplied by the preparation time (X), from the horizontal range (RH) as shown in Equation 2. The value ofthe horizontal range (RI-I2) to the point C is obtained by subtracting the distance BC, which represents the speed of the target (St) multiplied by the time of flight (t), from the horizontal range (RH3), as shown in Equation 5.

The value of X -St is obtained by the conventional multiplier 13, the inputs of which are shafts l4 and I6, movement of which represent target speed (St) and preparation time (X) respectively. The output shaft 14 of multiplier 13 is connected to shaft ID by differential 15. The movement of output shaft 16, of differential 15, represents the horizontal range (RH3) The value of t-St is obtained by the conventional multiplier 11, the inputs of which are shafts l4 and 20, whose movements represent target speed (St) and time of flight (t) respectively. The output shaft 18 of multiplier 11 is connected to shaft 16 by differential 19. The movement of the output shaft 80, of differential 19, represents the horizontal range (EH2).

It will thus be seen that the movement of shaft 16 of Fig. 3 corresponds to the movement of shaft 34 of Fig. 2 and the movement of shaft of Fig. 3 corresponds to the movement of shaft 23 of Fig. 2.

The constructions and the arrangements of parts shown in Fig. 3 are otherwise identical with those shown in Fig. 2.

It is obvious that various changes may be made by those skilled in the art in the selection of mechanisms and the mode of operation. For example, should it be desired to utilize the invention to fire a barrage for a period of time of Y seconds duration, the arbitrary preparation period (X) may be increased for computing purposes to a pseudo value (X) equal to the true preparation time plus one-half the barrage time as expressed in the equation rem- 10 When the pseudo value (X) is used in the setting of the preparation time input the super elevation, deflection and fuse setting will be computed for the position of the target at the ex- If the sights and fuses are set in accordance with the computed values and the sights of the gun are kept on the target throughout the barrage time the points of burst of the projectiles will follow a curved path intercepting the path of the target at a point X+t seconds after the observation time. This curve is indicated by the broken line passing through the point C of Fig. 1.

I claim:

1. A closed system fire control computer, for a gun firing at a target approaching at a constant height above a horizontal plane, comprising a vector analyzer including a pair of movable component members and a rotatably mounted disk having a radial range scale thereon representing direct range, means for rotating the disk to angularly position the range scale in accordance with the elevation angle of the target position at an observing instant, means to adjust the component members relative to the disk to positions representative of the horizontal range and height components corresponding to the direct range and the elevation angle of the target at the observing instant, a multiplier including input members settable in accordance with the speed of the target and the period of time of flight of the projectile and an output member positioned thereby, a second multiplier including input members settable in accordance with the speed of the target and a selected preparation period of time and an Output member positioned thereby, means for combining the movement of said multiplier outputs with the movement of the horizontal range component member at the observing instant for moving a pair of elements in accordance with the horizontal ranges of the target at the end of the respective periods, a pair of vector means settable by the movement of the respective elements and the height component member of the vector analyzer, and having outputs, the movements of which are proportional to th angles of elevation of the target at the end of the respective periods, means for combining the outputs of said pair of vector means for determining the vertical angular deflection, ballistic computing means settable in accordance with the position of the element representing the horizontal range of the target at the end of the flight period and in accordance with the position of the height member for determining the position of outputs representing the super elevation of the gun and the flight period, and means operably connecting the output of the ballistic computing means representing the fiight period to the input member of the first mentioned multiplier settable in accordance with the period of time of flight of the projectile.

2. A closed system fire control computer, for a gun firing at a target approaching at a constant height above a horizontal plane, comprising a vector analyzer including a pair of movable component members and a rotatably mounted disk having a radial range scale thereon representing direct range, means for rotating the disk to angularly position the range scale in accordance with the elevation angle of the target position at an observing instant, means to adjust the component members relative to the disk to positions representative of the horizontal range and height components corresponding to the direct range and the elevation angle of the target at the observing instant, a multiplier including input members settable in accordance with the speed of the target and the period of time of flight of the projectile and an output member positioned thereby, a second multiplier including input members settable in accordance with the speed of the target and a selected preparation period of time and an output member positioned thereby, means for combining the movement of said multiplier outputs with the movement of the horizontal range component member at the observing instant for moving a pair of elements in accordance with the horizontal ranges of the target at the end of the respective periods, a pair of vector means settable by the movement of the respective elements and the height component member of the vector analyzer, and having outputs, the movements of which are proportional to the angles of elevation of the target at the end of the respective periods, means for combining the outputs of said pair of vector means for determining the vertical angular deflection, ballistic computing means settable in accordance with the position of the element representing the horizontal range of the target at the end of the flight period and in accordance with the position of the height member for determining the position of outputs representing the super elevation of the gun and the flight period, and means settable in accordance with the position of the output of the ballistic computing means representing the super elevation for determining the angle of drift of the projectile, andmeans operably connecting the output of the ballistic computing means representing the flight period to the input member of the first mentioned multiplier settable in accordance with the time of flight of the projectile.

3. A closed system fire control computer, for a gun firing at a target approaching at a constant height above a. horizontal plane, comprising a vector analyzer including a pair of movable component members and a rotatably mounted disk having a radial range scale thereon representing direct range, means for rotating the disk to angularly position the range scale in accordance with the elevation angle of the target position at an observing instant, means to adjust the component members relative to the disk to positions representative of the horizontal range and height components corresponding to the direct range and the elevation angle of the target at the observing instant, a multiplier settable in accordance with a selected preparation period of time and the speed of the target for positioning an output in accordance with the change in horizontal range of the target during the said period, a second multiplier settable in accordance with the period of the time of flight of the projectile and the speed of the target for positioning an output in accordance with the change in horizontal range of the target during the said period, means for combining the movement of the output of the first mentioned multiplier with the movement of the horizontal range component member for obtaining an output representing the horizontal range of the target at the end of the preparation period, means for combining the movement of the output of the second multiplier with the output representing the horizontal range of the target at the end of the preparation period, for obtaining an output representing the horizontal range at the end of the period of the time of flight, a pair of vector means settable by the outputs of the combining means and the height component member of the vector analyzer for determining the angles of elevation of the target at the end of the respective periods, means for combining the outputs of said. pair of vector LOU.

means for determining the vertical angular defiection, ballistic computing means settable in accordance with the position of the output representing the horizontal range of the target at the end of the flight period and in accordance with the height component member for determining the position of outputs representing the super elevation of the gun and the flight period, and means operably connecting the output of the ballistic computing means representing the flight period to the second multiplier to effect the setting in accordance with the period of the time of flight of the projectile.

4. A closed system fire control computer, for a gun firing at a target approaching at a constant height above a horizontal plane, comprising a vector analyzer including a first component slide movable to a position representative of the horizontal range component of the target position, a second component slide movable to a position representative of the height component of the target position and a rotatably mounted disk having a radial range scale thereon representative of the direct range of the target, means for rotating the disk to angularly position the range scale in accordance with the elevation angle of the target position at an observing instant, means to adjust the slides to positions relative to the disk representative of the horizontal range component and the height component corresponding to the direct range and elevation angle of the target at the observing instant, means movable in accordance with a selected preparation period of time, means movable in accordance with a computed period of time of flight of the projectile,

a first multiplier settable by the preparation period means and in accordance with the speed of the target, a first differential for combining the output of the first multiplier and the movement of the said first component slide, a second multiplier settable by the flight period movable means and in accordance with the speed of the target, a second differential for combining the outputs of the first diiferential and the second multiplier, a first ballistic computing means settable by the second component slide and the output of the second difierential for determining the flight period and having an output movable in proportion thereto, means connecting the output of the first ballistic means to the flight period movable means, a first vector means settable by the output of the first differential and by the said second component slide, a second vector means settable by the output of the second diiferential and by the said second component slide, a third differential for combining the outputs of the first and the second vector means, a second ballistic computing means settable by the second component slide and the output of the second differential for positioning an output in accordance with the super elevation of the gun, and a fourth difierential for combining the outputs of the second ballistic means and the third difierential whereb the output of the fourth differential represents the desired elevation angle between the gun and the sight.

5. A closed system fire control computer for a gun firing at a target approaching at a constant height above a horizontal plane, comprising a member settable in accordance with the horizontal range of the target at an observing instant, a member settable in accordance with the height of the target, a multiplier including input members settable in accordance with the speed of the target and the period of time of flight of the projectile and an output member positioned thereby, a second multiplier including input members settable in accordance with the speed of the target and a selected preparation period of time and an output member positioned thereby, means difierentially connecting the multiplier outputs with the horizontal range member for positioning a pair of elements in accordance with the horizontal ranges at the end of the respective periods, a pair of vector means positioned by the respective elements and the height member and having outputs the position of which are proportional to the angles of elevation of the target at the ends of the respective periods, means differentially connecting the outputs of said vector means for determining the vertical angular deflection, ballistic computing means actuated in accordance with the position of the element representing the horizontal range at the end of the time of flight period and in accordance with the setting of the height member for determining the position of an output representing the period of time of flight of the projectile, and means operably connecting the output of the ballistic computing means to the input member of the first mentioned multiplier settable in accordance with the period of the time of flight of the projectile.

GEORGE ALFRED CROWTHER. 

